Recent additions to the 3rd Generation Partnership Project (3GPP) standard include provisions directed towards Multimedia Broadcast Multicast Services (MBMS) and Enhanced MBMS (eMBMS). The MBMS and eMBMS protocols are intended for a variety of broadcast and multicast services, such as mobile TV and radio broadcasting to be delivered to users with existing 3GPP network wireless resources. As these services use wireless network resources, the reception quality of MBMS and eMBMS is dependent on the radio link quality that a User Equipment (UE) with a serving cell. UEs experiencing poor radio link conditions may correspondingly experience a low quality of eMBMS reception.
The geographic placement of eMBMS-enabled cells may be non-uniform, and accordingly the service area of eMBMS may vary significantly. For example, eMBMS may only be available in specific geographic locations, and accordingly may only be available to nearby users. Furthermore, the availability of eMBMS may vary over time, as specific eMBMS-enabled cells may only provide eMBMS transmissions during certain times, such as e.g. during a particular event. Additionally, different geographic groups of eMBMS-enabled cells may provide different eMBMS streams. Consequently, a user may only be able to access specific eMBMS streams in certain areas dependent on whether the nearby eMBMS-enabled cells are broadcasting the specific eMBMS stream.
A user may therefore experience geographic regions where a particular desired eMBMS stream is not available. Additionally, a user may experience geographic regions where no eMBMS service is available at all. A user who is engaged in an eMBMS session (i.e. receiving a specific eMBMS stream) and subsequently leaves the eMBMS service area may thus experience a significant decrease in the reception quality of the eMBMS stream or even have the active eMBMS session terminated completely. A user who is leaving the eMBMS service area may therefore wish to maintain an existing eMBMS connection at high quality for as long as possible. In other words, a user may desire to stay continue receiving a desired eMBMS stream by maintaining a connection to the respective transmitting eMBMS-enabled cell instead of performing cell reselection to a cell that does not provide the desired eMBMS stream (i.e. a non-eMBMS cell or an eMBMS cell that is not providing the desired eMBMS stream). A user may thus wish to maintain reception of an existing eMBMS stream even if an incompatible cell (i.e. a non-eMBMS cell or an eMBMS cell that is not providing the desired eMBMS stream, as will be referred to hereafter) may be able to provide a higher level of conventional cellular service (such as e.g. voice or data). A user may additionally desire to forego measurement gaps due to the negative effects these measurement gaps may have on the reception quality of the desired eMBMS stream.
However, the current 3GPP standard does not consider active eMBMS sessions in the decision to perform neighbor cell measurements or cell reselection from a UE in idle mode. For example, the current Long Term Evolution (LTE) standard dictates that a UE in idle mode is to initiate neighbor cell measurements and/or cell reselection based on serving cell signal power and signal quality measurements. The LTE standard specifies periodic measurements of the Reference Signal Receive Power (RSRP, i.e. signal power) and Reference Signal Receive Quality (RSRQ, i.e. signal quality) of a reference signal received at a UE from the serving cell. The UE may then compare the measured RSRP and/or RSRQ values to network-provided thresholds to determine if neighbor cell measurements and/or cell reselection is necessary. A UE may be instructed by the network to perform neighbor cell measurements of nearby cells or cell reselection if the measured serving cell RSRP and/or measured serving cell RSRQ falls below the network-defined thresholds, which may indicate a reduced quality of service for the user. The thresholds may be network-provided, and the cell reselection thresholds may be lower than the neighbor cell measurement threshold to ensure neighbor cell measurements will typically be performed prior to reselection.
The standard thus does not consider the presence of active eMBMS streams when determining if neighbor cell measurements and/or cell reselection is appropriate. The standard also does not consider whether nearby candidate cells (e.g. for cell measurement and/or reselection) are capable of providing the active eMBMS stream. A user may therefore be engaged in an eMBMS session and may be leaving the serving area of the current cell and entering the service of area of a nearby incompatible cell (i.e. a cell that does not provide eMBMS or is not providing the active eMBMS stream). As the user is leaving the service area of the serving cell, cell measurements may be triggered on nearby candidate cells, including the nearby incompatible cell. Consequently, the user may experience a drop in eMBMS stream quality due to the performance of standard-dictated measurement gaps required to measure nearby candidate cells. The measurement gaps may even be used to search and measure incompatible cells (i.e. non-eMBMS cells or eMBMS cells that do not provide the desired eMBMS stream), such as the incompatible cell which the user is entering the service area thereof. In addition to a reduction in eMBMS stream quality, the UE may select the incompatible cell as the new serving cell, thereby terminating the active eMBMS session. A user may thus not wish to perform measurements on incompatible cells if an eMBMS session is active, or may wish to wait until absolutely necessary to consider incompatible cells for measurement. Furthermore, a user may wish to not perform reselection to an incompatible cell if an eMBMS session is active, or may wish to wait until reselection is absolutely necessary to consider incompatible cells for reselection. It therefore may be advantageous for a UE to consider whether or not an eMBMS session is active as well as the eMBMS capabilities in the decision to initiate cell measurements and cell reselection.